Toggle Flipflops

Binary counters are made up of toggle flipflops. In Quartus, here is what the toggle flipflop (tff) looks like. Note that the triangle on the signal on the lower left side indicates the clock signal.

Depending on what is connected to the inputs, the tff behaves in different ways. Here is a table from the help pages, describing the behavior of the tff with different signals attached to the inputs. Note that we are interested in having the output signal (Q) toggle.

The table below shows the default values of the signals if nothing is attached to them. So, while the default value of CLRN and PRN is VCC (and this is what we want for our toggle flipflop), it is good practice to still connect a VCC to these signals.